And yet, this is the vision of the future space age, that in another few decades, or a century at most, private corporations will be able to afford to run manned Mars missions out of their operating budget.

This also means that otherwise-minded private groups will have the wherewithall to wage high-tech war, which is why the social and political side of terrorism, cults, fanatics, and social misfits need to be addresses, not just trying to lance the resulting unsightly boils.

After all, if you envisage humanity spreading across the Solar System and moving asteroids around for processing, Larry Niven's apocalyptic vision of the Mote in God's Eye may come true - that one faction may steer bolides at targets on the home planet - as blackmail, power play, terrorism, or simply a "final solution".

These things will come to pass, unless we change the nature of society.